The present invention relates to a solid-state image pickup device. Image pickup tubes are most extensively employed as image pickup devices. In addition to image pickup tubes, recently, area image sensors have been used. The area image sensors include MOS, CCD, CPD and BBD types. These elements have a wide range of application because, compared with the image pickup tube, they are small in size, light in weight, semi-permanent in service life and low in power consumption.
There are many cases in which an area image sensor is used to convert an optical variation into an electrical signal, namely, a video signal, whereby the picture is reproduced on a television monitor according to the electical signal, or the video signal is recorded with a VTR. In this connection, optical variations in a sensed image are converted into a video signal. To produce a still picture video signal, an exposure time such as 1/30 second or 1/60 second is employed. That is, the exposure time of the area image sensor is fixedly set at 1/30 second or 1/60 second. Accordingly, in the case when the image light is high in intensity, the exposure may be saturated, and hence blooming may result. Even if the exposure is not saturated, vertical smearing is liable to occur.
These difficulties also occur in the case in which an ordinary image pickup tube is used. That is, since the time for the image pickup tube to integrate the image light is fixed as described above, the quantity of light is inadequate when the image is dark and it is excessive when the image is bright.
In view of the foregoing, an object of the present invention is to provide a solid-state image pickup device in which, in producing a still picture video signal with an area image sensor, no blooming or vertical smearing occurs.